Low melting glass and compositions containing the same



United States Patent 3,480,566 LOW MELTING GLASS AND COMPOSITIONS CONTAINING THE SAME Lewis C. Hoffman, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 22, 1965, Ser. No. 502,486 Int. Cl. H01b 1/00; C03c 3/30 US. Cl. 252-514 4 Claims ABSTRACT OF THE DISCLOSURE PbO-Bi O -B O -SiO glasses, to which this invention in part relates, are well-known silver binders. Knox, US. Patent 2,385,580, for example, describes their use in conjunction with silver as metalizing compositions in the manufacture of electrical devices. The glasses disclosed by Knox have melting points of about 650 C. and generally wet ceramic substrates poorly with a high contact angle of about 25 to 30. There is no mention in Knox or other known prior art of the inclusion of W0 and/or V 0 in vitreous compositions employed in the making of electrical components. Beck and Taylor in US. Patent 2,853,393 disclose the use of W0 as an additive in PbO-B O -P O glasses. The W0 was disclosed in this patent as used in relatively large percentages to provide high refractive index gem-like glass compositions. No mention was made of the melting point or wetting qualities of these glasses. Brekhovskik-h has disclosed in Glastech Ber. 32, 43742 (1959) that V 0 has been added to PbO-BizOg-SIOZ glass and Bl203'B203'SiO2-P205 and -Ge0 glasses with the resulting formation of nonglass compositions.

It is an object of this invention to provide novel glasses with excellent wetting and softening properties which can be used with great advantage in the manufacture of electrical circuits and circuit components. It is a further object of this invention to provide overglazing and metallizing compositions comprising these glasses which can be used in the manufacture of electrical circuits and components thereof. Still other objects of the invention will be obvious to those skilled in the art reading the following detailed description of the invention.

All of the objects of this invention are achieved through the use of vitreous compositions consisting essentially of 15 to 75 weight percent of Bi O 6 to 82 weight percent of PbO, 0 to 7 weight percent of B 0 and 0 to 10 weight per cent of SiO the sum of the Si0 and B 0 present being within the range of 1 to Weight percent and either 1 to 10 weight percent of W0 or 1 to 5 weight percent of V 0 The overglazing compositions of this invention comprise the above vitreous compositions and liquid vehicles wherein the amount of vehicle preferably does not exceed 60 percent by weight of the overglazing compositions. The metallizing compositions comprise finely divided powder of the above vitreous compositions in the weight percent range of from 7.5 to 30 percent, powders of finely divided noble metal particles in the weight percent range of from 30 to 75 percent and a liquid vehicle in the weight percent range of from 15 to percent.

The novel vitreous compositions of this invention are made by mixing or adding together known batch constituents and heating the batches to form the glasses. In preparing the batches from which the glasses of this invention are formed, Bi O can be added as such, PbO as litharge or red lead, B 0 as boric acid and SiO;, as glass sand or potters flint. W 0 can be added as tungstic acid anhydride and V 0 can be added as ammonium vanadate or vanadium pentoxide. In each case the amounts of batch constituents are adjusted to yield the amounts of oxides required by the weight percent composition of the glass desired.

The glass compositions of this invention were prepared by melting gram batches to homogeneity in kyanite crucibles at 1200 C. and pouring out 2 cm. diameter discs onto steel plates. All the discs cooled without opacifying, were homogeneous and single phase. The compositions were accordingly regarded as glass forming. The compositions were then tested to determine the value of various physical characteristics related to their use as overglazing and metallizing compositions.

Densities were measured by the method of Archimedes, using glass fragments. The fragments were weighed, then placed in water to displace an equal volume thereof.

Thermal expansions and softening points were measured in a fused silica apparatus consisting of a piston inside a cylinder resting on a three inch by /2 inch diameter bar of the glass. The extension of the silica rod was transmitted to an axis of an x-y recorder by means of a variable transformer. Temperature was fed to the other axis of the recorder by means of a thermocouple. The thermal expansion was calculated from the average slope of the curve in the range of 0-200 C., extrapolated where necessary. The softening point was taken as that temperature at which the x-y recorder trace showed a reversal of slope.

The contact angles were measured on alumina plates heated by means of platinum strip resistor to 750 C. Temperature was measured by an optical pyrometer and the contact angle by an optical magnifying apparatus fitted with a calibrated eyepiece. The angle measured was advancing in all cases. The alumina plates employed were the commercially available AlSiMag 6 14, manufactured by American Lava Co., Chattanooga, Tennessee. Other substrates, including those composed of forsterite, sapphire, steatite, titanium dioxide, alkali earth titanates or zircon porcelain, showed improved wetting with the compositions of this invention, similarly as did the alumina substrate.

Table I, set forth herebelow, identifies novel compositions of this invention by weight percent of their ingredients and lists together therewith data obtained as above indicated on density, thermal expansion, softening point and contact angle measured at 750 C. All of the examples set forth have utility in overglazing and metalizing compositions. The table also sets forth the ranges of ingredients usable in the practice of the invention.

TABLE I.-COMPOSITIONS, W'I. PERCENT Examples B1 0 75.5 54.5 15.0 15.0 15.0 3. 47.0 44.0 47.0 PbO 5.5 42.0 81.5 30.5 72.5 0. 47.0 47.0 45.0 B203 5.5 1. 25 1. 25 1. 25 1. 25 2. 4.0 4.0 4.0 sio 5.5 1.25 1.25 1.25 1.25 2.0 W05-.- 5.0 1.0 1.0 2.0 10.0 5 20 V D e 1 1 s.,gr./ec 5.782 5. 914 7.321 7.217 5. 923 5. 945 7.143 7.210 7. 938 Thennelexp, p.p.m./C 12.5 13.4 12.3 13.1 13 2 11.5 12.7 14.5 15.2 Soft. pt o 252 270 280 285 315 255 280 285 255 Cont. angle at 750 0. degrees 21 16 4 3 12 18 9 32.0 32.0 32.0 63.0 53.0 51.0 50.0 58.0 20.0 20.0 4.0 4.0 4.0 5.0 10.0 10.0 5 3.0 4.0 5.0 2.0 2.0 "I 7:2507354 1103"53177325 .5 13.8 13.8 12.5 14.1 14.2 o 245 255 270 310 300 300 310 320 340 Cont. angle at 750 0. degrees. 14 12 15 11 15 18 20 23 17 20 22 Compo- Compositions sitions 0011- COD-- Examples All eompotaining taining sitlons, V105, W01, 23 24 25 26 27 28 range range range B1203 49.0 49.0 32.0 73.0 32.0 32.0 PbO..- 45.0 45.0 54.0 20.0 59.0 51.0 B203.-- 2.0 S102-.. 2.0 4.0 2.0 5.0 4.0 4.0 W0 2.0 5.0 3.0 V205 2.0 2.0 2.0 Dens., gr./ec 7.842 7.535 7. 243 5. 943 7. 439 5.940 Thermal exp., m/C 14.7 14.2 15.0 11.8 14.2 15.1 Soft. pt.,O 275 280 250 255 255 270 Cont angle at 750C degre 8 11 15 18 12 11 The compositions in which PbO and Bi O are present erably an organic solvent is used, with or without thickin about the same amounts, e.g., Nos. 9, 10 and 11, are ening agents, stabilizing agents or the like. Examples of preferred for their combination of stability as glasses, such solvents are methyl, ethyl, butyl, propyl and higher low softening points and good wetting qualities. Comalcohols, the corresponding esters of these alcohols such positions high in PbO show the next most attractive as the acetates, propionates, etc., the terpenes, and liqcombination of properties and those high in Bi O are uid resins such as pine oil, alpha-terpineol and beta-terlast in order of preference. One of the major contribupineol. Other liquids almost without limit may be used; tions of W0 and V 0 is their ability to increase the the function of the liquid is mainly to form a paste or wetting of ceramic substrates at a given temperature. liquid of the desired viscosity for application purposes. The beneficial effect of V 0 and W0 is thought to The vehicles may, in addition to the above ingredients, come about from the high ratio (at least 2.5 to 1) of contain or be composed of volatile liquids which promote oxygen ions to cations in these oxides. While there are fast setting after application. other metals in the periodic table which form oxides with As thickening agents, ethylcellulose and methyl and high amon to cation ratios, none other than vanadium or b l methacrylate resins may be emp1oyed Solutions u t are 1 known 9 pp t Whwh 01161- a r of from 1-10 percent by Weight of ethylcellulose in beta. blnatlon 0f h OXYgeII 9 t0 Cation ratio and Whlch terpineol are preferred and have been used in the folare weak and will not contnbute to the forces holding the l i examples,

5+ 5+ f h T 23 forces of 4; The glasses of this invention together wlth appropriate fo eir argedsizes h e P F 0 ca 1011 16 vehicles are applied by any desired method to ceramic bormls1 an 07111 e Wltf 1? 15 rang i amons g i substrates, with or without circuit components, such as f e 9 1 a o 6 2 25 capacitor conductors and resistors printed thereon. The e d Whlc, a S tot 6 9 e1ve 2 0 e m ten Su methods commonly used are dipping, banding, spraying i H1ghlygherent lqmds 1 vlsFoslty are less and screen-stenciling. The glasses may be employed in ikgly to wet su strates than are liquids whlch are Weakly molten form as the sole ingrediflnts of dipping composi co erent' tions. The glasses in frit form may be dispersed in vehi- The compositions set forth in Table I are useful as cles such as 2 percent solutions of ethylcellulose in beta overglazing glasses 1n the encapsulat ng of hybrid circuits terpineol to provide dipping slurries. Dipping slurries and in the formation of dielectrlcs in printed capacitors. comprising glass frits and vehicle generally contain about {as previously indicated, they may also be used as binders 50% inorganic solids. Banding or rotating wheel appli- 1n metalizing compositions. To be used in these manners, cator vehicles are slightly more viscous than the fluid the glasses are most usually prepared as frits so that they dipping variety and an example thereof is a 4% by may be readily comminuted to small particles, dispersed in weight solution of ethylcellulose in beta terpineol. Spraylnert vehlcles and applied as enamels. The glass batch ing vehicles are generally based on aqueous solutions of components, as indicated above, are melted to homoge- 2% by weight methylcellulose. Organic solvent spray vene 1ty in kyanite, alumina or platinum crucibles and then hicles are rare. Screen-stencil vehicles are the most viscous fritted by being poured into water. The frits are recovered of all. An 8% by weight solution of ethylcellulose in from the Water and ball milled in normal fashion until beta terpineol is a good example of a screen-stencil vehitheir average particle sizes are about 10 microns. The cle. In all instances, the amount of vehicle used is suffr1ts are then filtered from the mill water, dried and ficient to enable the glass composition to be readily and combined with the proper vehicles. properly applied; excessive amounts of vehicle require As a vehicle, any inert liquid may be employed. Preflonger drying periods and are an unnecessary expense.

6 Several examples of the use of the glasses of this into cover only the resistors. Firing at 450 C. for 2-3 vention in overglazing compositions, including composiminutes gave less than /2 change in electrical resistance tions used for capacitor dielectrics formation, are set forth and produced moistureaproof, gas-proof coatings. Unproherebelow. tected resistors exhibited large changes in the electrical EXAMPLE 29 5 resistance when tested separately in high humidity and Application by dipping into the melt hydrogen atmospheres. The resistors coated in accordance with this example showed no significant resistance Frrts prepared as described above from compositions change when i il l testei 2-5 were found to be particularly suited for application by the melt dip method. The frits of these four exam- EXAMPLE 33 U ples were separately melted at a relatively high tempera- Applwation y scffien'stenclhng lure, and then 10Wfed p y to a temperature Frit of composition 1 is a particularly suitable dielectric about abOVe their Softening P Their material. Printed capacitors were formed by stenciling a peratures were then adjusted until their viscosities were 1 i 1 mta1 electrode on a fl t alumina Such that Parts thereof did not form Strings on femov' strate, overstenciling with a screen-stencil composition al from the molten bath. Fired printed circuit elements f 0% f it of composition 1 d 8% ethylcellulose in containing Pd-PdO'Ag'kad borosilicate resistors and beta terpineol, then overstenciling a second electrode of Au conductors forming a resistive capacitance network p1atinum-go1d composition I h bl of some of on alkaline earth titanate ceramic substrates were prethe capacitors, h layer was fir d separately; i other heated to about 150 C. to minimize thermal shock and instances, all three layers were b h to maturity at were then rapidly dipped into the molten glasses, held once by simultaneous firing at temperatures from 450- there for 1-5 seconds and removed and allowed to cool. c and films f 5 to 0 minutes Ten thousand Thin layers of glass remainfid 011 the circuit elements and picofarads per square inch of 0.001 inch thick dielectric solidified 9 Cooling to Provide fixcenent gastlght, were obtained repeatedly in all instances with dissipation metlc coatmgsfactors between 1 and 2 percent. The dielectric constant EXAMPLE of the glass calculated from these capacitors was 270. A n i b di i The metalizing compositions of this invention contain an inert vehicle, a noble metal powder and binder components in finely divided form. These compositions will generally contain 90 to 50 percent by weight noble metal powder, e.g., silver, gold, palladium, platinum, rhodium, osmium or iridium or mixtures or alloys of two or more of such metals and 50 to 10 percent by weight of the hinder, the vitreous compositions of this invention. These percentages are based on the combined weights of noble metal and binder present.

Frits prepared from compositions 6-10 were separately ball milled, dried and dispersed in 2% solution of 30 ethylcellulose in beta terpineol to provide 50% frit solids slurries. Chip active devices, silicon diodes, were dipped into the slurries, removed, allowed to drain and then fired at 350 C. for 1-2 minutes. This short time-temperature exposure did not adversely affect the active device parameters and provided an inexpensive, durable, gas-tight coating.

EXAMPLE 31 Noble metal powders having a particle size not exceeding microns in diameter are generally usable and Application by banding 40 those of particle sizes ranging from 0.05 to 10 microns spiraled end capped rod resistors were banded so that are preferred. Binder particles of a particle size not exonly the resistor portions which consisted of Pd-PdO- ceedmg mlcrons. 1n dmmete? i generally usable but Ag-lead borosilicate glass were covered with slurry when those to 15 95 are dlstmctly the resistors were contacted with the upper portion of a Metahzmg compostlons wer e prepared usmg a F slowly rotating aluminum disc whose lower portion moved 45 bar of the above glass compgsltlonsg 'apphed to alumlna through a banding slurry. Ten banding slurries, each substrates, fired and tested for adhesion thereto. Table II.

comprised of an 80% dispersion of the frit of one of herebelow Sets forth Y of the nobl? metal the compositions 11-20 and a 4% ethylcellulose-beta ter- Powders and E I compositions Whlch were used form pineol solution were used to coat diiferent resistors. After the zlng compositions. The metal powders condrying the coated resistors were fired at for sisted essentially of particles having sizes within the range minutes. The resistance values of these resistors changed 00 P to 10 mlcrons- The glass FomPosltloni were fntted less than the acceptable 1% during the overglazing appliand than P to partlcl? $1735 of about 1 15 cation and firing The coatings formed were gas tight microns. The metalizing compositions were stenclled and durable through a 200 mesh screen onto the alumina substrates,

dried and fired for 2 minutes at temperatures 100 C. above the softening point of the glass composition constituent of the metalizing composition which values are Frits of compositions 21 and 22 are particularly suited reported in Table Adhesion was determined Solderfor screen-stenciling over Pd-PdO-Ag-lead borosilicate g -0 tinned C pp r l ad Over approximately 0.10 glass resistors on flat substrate microcircuits. Separate in h f its ngth t the metalizin'g composition and pull- EXAMPLE 32 Application by screen-stenciling slurries of these compositions were prepared, each cong 01f the lead with an I s on tester in peel. The taining an dispersion of the frit of one of the comvalues of adhesion reported in Table II reflect the adpositions in an 8% ethylcellulose-beta terpineol solution. hesive pull in pounds per square inch which was with- These slurries were applied through a screen-stencil so as stood by the metalizing composition-substrate bond.

TABLE II.METALLIZING COMPOSITIONS, WT. PERCENT Examples Gold powder 60.17 Platinum powder Palladium powden Silver powder Glass binder (Table I) 8% ethylcellulose in beta terpineol Adhesion, p.s.i

Having described various embodiments of the invention for purposes of illustration rather than limitation, what is claimed is as follows:

I claim:

1. A metallizing composition suitable for use in the manufacture of electrical circuits Comprising, by weight, 30-75% of a noble metal powder, 15-40% of a liquid vehicle and 75-30% of a glass which consists essentially of 1575% Bi O 6-82% PbO, -7% of B 0 and 0-10% of SiO the sum of SiO and B 0 always being 115%, and a metal oxide selected from the group consisting of 15% V 0 or 110% W0 2. A metallizing composition suitable for use in the manufacture of electrical circuits comprising, b weight, 90-50% of a noble metal powder and 50-10% of a glass which consists essentially of 15-75% Bi O 6-82% PbO, 0-7 of B 0 and 0-10% of Si0 the sum of SiO and B 0 always being 1-15%, and a metal oxide selected from the group consisting of 1-5% V 0 or 1-10% W0 wherein the percentages are based on the combined weight of metal powder and glass present.

3. A metallizing composition suitable for use in the manufacture of electrical circuits comprising 30-75% by weight of a finely divided noble metal powder, 15- 40% by weight of a liquid vehicle and 75-30% by weight of a glass which consists essentially of 15-75% by weight Bi O 6-82% by weight PbO, 0-7% by weight B 0 010% by weight SiO the sum of SiO and B 0 always being 1-15% by weight, and 110% by weight W0 4. A metallizing composition suitable for use in the manufacture of electrical circuits comprising -75% by weight of a finely divided noble metal powder, 1540% by weight of a liquid vehicle and -30% by weight of a glass which consists essentially of 15-75% by weight Blgog, B203, 010% by weight SiO the sum of SiO and B 0 always being 1-15% by weight and 1-5% by weight V 0 References Cited UNITED STATES PATENTS 2,385,580 9/1945 Knox 106-49 2,713,286 7/1955 Taylor 106-47 2,853,393 9/1958 Beck et a1. 106-47 JAMES E. POER, Primary Examiner U.S. Cl. X.R. 

